Calcium is a ubiquitous element found in many art materials, including pigments. This lesson focuses on the role of calcium in painting preparation layers, pigments, and paper manufacturing. By exploring its presence and analyzing spectra, we gain insights into the applications and limitations of calcium in pigment identification.
Objectives
- Understand the presence and roles of calcium in painting preparation layers and pigments as a filler.
- Explore the application of XRF spectroscopy to detect calcium in different materials.
- Analyze historical changes in calcium use in paper manufacturing through spectra comparison.
Materials
- Pigments Checker: acrylic binder, chalk, bone black.
- Samples:
- Historical papers (16th, 18th, 19th century)
- Modern copy paper
- XRF spectrometer (no-filter setup)
Lesson Plan
1. Introduction to Calcium in Artistic and Historical Materials
- Discuss the prevalence of calcium in painting preparation layers.
- Examples: Gypsum-based layers (calcium sulfate) in Italian Renaissance paintings; calcium carbonate layers in Northern European art.
- Explain calcium as a filler in pigments and its implications for XRF analysis.
- Note that calcium signals often originate from the ground preparation or filler rather than the pigment itself.
2. Application of XRF Spectroscopy in Calcium Analysis
- Introduce calcium’s K-alpha (3.7 keV) and K-beta (4 keV) peaks, emphasizing their separation and detectability.
- Use the Pigments Checker to demonstrate calcium detection:
- Test a cardboard sample with an acrylic binder, highlighting strong calcium signals.
- Analyze chalk (calcium carbonate) and compare spectra, noting the prominent calcium peak.
- Examine bone black pigment and discuss its calcium phosphate content from charred bones.
3. Case Study: Calcium in Historical and Modern Paper
- Analyze paper samples from different centuries using XRF spectroscopy:
- 16th-century paper (1527): High calcium peak (30,000 counts).
- 18th-century paper (1799): Reduced calcium content.
- 19th-century notary paper (1898): Minimal calcium signal.
- Modern copy paper: Substantially higher calcium content.
- Discuss how calcium levels reflect changes in paper manufacturing technology and practices over time.
